Poliploid

Poliploid, or polyploid, refers to an organism that has more than two complete sets of chromosomes. In diploids, cells are 2n; polyploids have 3n (triploid), 4n (tetraploid), 6n (hexaploid), and higher multiples. Polyploidy can arise by genome duplication within a species (autopolyploidy) or by hybridization between species followed by chromosome doubling (allopolyploidy). It can also result from errors in cell division that produce unreduced gametes.

Polyploidy is especially common in plants and is a major driver of plant diversification and speciation. Many crop species are polyploid: bread wheat is hexaploid, potato is tetraploid, and cultivated strawberries are octoploid. Bananas are often triploid, contributing to their sterility and seedless fruit. In animals, polyploidy is less frequent but occurs in some groups, including certain fish, amphibians, and invertebrates.

Biological consequences of polyploidy include changes in cell size and organ dimensions, often leading to larger leaves or fruits. Polyploids may exhibit increased vigor or altered physiology and can show reproductive isolation from their diploid ancestors. However, odd numbers of chromosome sets can cause pairing problems during meiosis, reducing fertility; many naturally successful polyploids are even-numbered (tetraploid, hexaploid, etc.) or become fertile after genome stabilization.

In agriculture and horticulture, polyploidization is used to create new varieties with desirable traits, such as larger fruit, improved stress tolerance, or seedlessness. Techniques like chromosome doubling with certain chemicals are employed to induce autopolyploid or allopolyploid lineages for breeding.